1. Field of the Invention
The present invention relates to a medium replacement type disc apparatus and in particular, a medium replacement type disc apparatus such as floppy disc apparatus and an optical disc apparatus,
2. Description of the Related Art
Conventionally, in a disc apparatus, a head is made to follow a predetermined track on a disc surface by a head positioning control system using a phase compensation filter such as a read lag filter or PID compensator. Here, if in a medium replacable disc apparatus, a disc medium is fixed on the spindle, there arise a primary rotation period runout (deviation) due to a chucking error. However, for a conventional disc apparatus, positioning using a stepping motor has been sufficient, not requiring a high-precision accuracy.
Moreover, in a large capacity floppy disc apparatus, a voice coil motor (VCM) is employed for fetching a position error information from a disc medium surface. In such a large capacity floppy disc, a sufficient control band is obtained by a closed system using a phase compensation filter, assuring a compression ratio for the runout low dimensional rotation synchronized component, according to a necessary head positioning accuracy. However, when a larger capacity is desired, the track pitch is made smaller, and accordingly, it becomes difficult to assure a compression ratio of the runout low dimension rotation synchronized component.
On the other hand, a frequency rectifying filter is used as a filter for compressing the rotation synchronized runout. This is an application of the inner principle wherein a sinusoidal model is placed in a closed loop to increase the gain of the rotation synchronized component, so as to improve compression ratio characteristic of the frequency of the rotation synchronized component. (Advanced Methods for Repeatable Runout Compensation, IEEE Transaction on Magnetics, Vol. 31, No. 2, March 1995).
In general, when measuring a runout amount of a predetermined frequency, this frequency rectification filter need to fetch an amplitude and phase data at least over one cycle. Moreover, in order to compress the runout rapidly, the frequency rectifying filter should have an increased gain. However, the gain increase is not preferable, there is a danger of lowing stability of the system. To cope with this, when the runout is greater than a predetermined value for the track pitch, a data of several cycles is required in order to fetch frequency rectification filter parameters. For example, in case of a disc apparatus of 3000 rpm, when compressing a primary rotation synchronized runout, it takes 20 msec for one disc turn. Actually, it takes a time much more than this for fetching the parameters, thus increasing the disc apparatus rise.
That is, when using the aforementioned frequency rectification filter, which in principle measures a an amplitude and phase of a particular frequency and compresses the frequency, if no initial parameter is present, a parameter fetch time of one cycle or more is required. Accordingly, immediately after the rise of an apparatus, it is impossible to obtain the runout compression filter and it takes time for head positioning. This problem becomes especially acute in a disc apparatus having a power save mode. In a disc apparatus, for power saving and disc and head wearing prevention, if no access is made to the disc for predetermined time, the head is unloaded from the disc surface and the spindle rotation is stopped. This is called power save mode. Especially in a disc apparatus for portable terminal, this mode is often set in, and reset from this mode should be performed rapidly.
It is therefore an object of the present invention to provide a medium replacement type disc apparatus employing a frequency rectification filter as a runout compression filter wherein upon disc rise, the frequency rectification filter can rise rapidly, and increasing the speed of rise of the entire apparatus.
The medium replacement type disc apparatus according to the present invention comprises: a spindle for rotating a disc; a head facing a track on the disc; a frequency rectification filter constituted by a sinusoidal wave model increasing a gain of a particular frequency component of a position error signal produced by the head; a phase compensation filter for generating a control input for the head to follow the track according to the output of the frequency rectification filter; a power amplifier for amplifying an output of the phase compensation filter; an actuator for moving the head with respect to the disc in its radial direction according to a drive signal amplified by the power amplifier; a main controller for performing drive control of the spindle and seek control of the head by the actuator according to an external access instruction; and a memory used for processing by this main controller,
wherein the main controller has a rotation angle detection function for detecting a rotation angle of the spindle, and before reducing rotation speed of the spindle, stores in the memory the state amount of the frequency rectification filter together with the rotation angle of the spindle at that moment, and accelerates the spindle and, after the spindle speed has reached a predetermined constant speed, monitors the rotation angle of the spindle, and when the spindle rotation angle becomes equal to the rotation angle stored in the memory, sets in the frequency rectification filter the state amount of the frequency rectification filter stored in the memory.
According to another aspect of the present invention, there is provided a medium replacement type disc apparatus comprising: a spindle for rotating a disc; a head facing a track on the disc; a phase compensation filter causing the head to follow the track according to a position error signal produced by the head; a power amplifier for amplifying an output of this phase compensation filter; an actuator for moving the head in the radial direction of the disc according to the drive signal which has been amplified by this power amplifier; a main controller for performing drive control of the spindle and head seek control by the actuator according to an external access instruction; a memory used for processing by the main controller; a frequency rectification filter constituted by a sinusoidal wave model; and an adder for adding the output of the frequency rectification filter to the position error signal produced from the head and supplying a resultant sum to the phase compensation filter;
wherein the main controller stores in the memory in advance the amplitude and phase of a particular frequency component of the position error signal over one periphery of the disc, makes always 0 the input of the frequency rectification filter, calculates the state amount of the frequency rectification filter from the amplitude and phase stored in the memory, successively sets the state amounts in the frequency rectification filter according to the rotation of the disc, so as to obtain an output of the frequency rectification filter, and
wherein the main controller, before reducing the rotation speed of the spindle, stores in the memory the state amount of the frequency rectification filter, accelerates the spindle, and after the speed has become constant, the main controller monitors the rotation angle of the spindle and when the rotation angle of the spindle is matched with the state amount stored in the memory, the state amount of the frequency rectification filter stored in the memory is set in the frequency rectification filter.
It is preferable that the main controller detect a rotation angle of the spindle according to the number of servo areas which have been passed by the head starting at the servo area serving as an index.
The motor for rotating the spindle may be a three-phase motor, and the main controller defines the index as a servo area passed by the head immediately after a predetermined phase of the three-phase motor is risen.
When the head is unloaded from a recording area of the disc, it is preferable that the main controller store in the memory a state amount of the frequency rectification filter and a rotation angle of the spindle.
It is preferable that a notch filter be provided between the phase compensation filter and the power amplifier, for reducing the resonance frequency gain.